Electric device



Nov. 15, 1938. c, G, SWT'H 2,137,198

ELECTRIC DEVICE Original Filed March 5, 1925 ,Z7ZUQ7Z607 672607.26615972173 6; W WVMW Patented Nov. 15, 1938 UNITED STATES PATENT OFFICEELECTRIC DEVICE Delaware Application March 5,

' 1925, Serial No. 13,146,

Renewed June 22, 1933 12 Claims.

This invention relates to gaseous discharge devices in which ionizationis a substantial factor and in which the current density issubstantially in excess of that in a glow discharge device. My inventionis particularly applicable for use as rectifiers.

Particular objects of the invention are to pass current at a lowpotential difference: between cathode and anode, to avoid excessiveheating of 10 the electrodes and associated parts by the cathode-anodecurrent, to produce ample electronic emission from the cathode, todirect the electronic discharge to the anode with minimum resistance, toavoid the necessity of using large 5 quantities of vapor yieldingmaterial, to prevent electronic conduction from anode to cathode inresponse to reverse potential as in rectifying, and in some cases toeliminate the space charge in the region of the anode.

In one aspect the invention comprises a low pressure or high vacuum tube(of the order of .01 mm. of mercury e. g.) containing a cathode having amuch higher pressure (of the order of .1 mm. of mercury e. g.)maintained in the region of its discharge surface by electric forces(electrostatic or magnetic or both) for the purpose of obtaining ampleelectronic emission. This difference of pressure is maintained by anobstruction between the electron source and the electron receiving area.the obstruction having an opening therethrough for the passage ofelectrons and the opening being so restricted that a diilerence ofpressure (or state of ionization) may be maintained on opposite sides ofthe obstruction. As will appear hereinafter the obstruction ispreferably formed as a part of the cathode. According to the presentinvention the aforesaid difierence in pressure may be maintained bycentrifugal action, preferably produced 40 by a magnetic field extendinglongitudinally of the axis of said opening, the field reacting with theelectric discharge to whirl the molecules (or atoms) of gas and build upa higher pressure near the inner periphery of the hollow cathode.

In another aspect the invention involves the use of gases havingdifferent facility of ionization or ionization voltages and themaintenance of a higher proportion of the more ionizable gas in theregion of the electron source (e. g. inside 50 the hollow cathode) thanin the region of the anode or other electron receiving region. This ispreferably accomplished by means of a porous or semi-permeable wall ormembrane, formed for example of carbon or quartz, or metal with holes 55small enough to restrict the gaseous transfer to the type known as purediffusion, through which the less ionizable gas may escape from theoathode (preferably solely by the phenomenon of diffusion) withoutpermitting the more ionizable gas to escape so readily or at all. Forexample, by using a mixture of helium and mercury vapor with a quartzwall, the helium escapes while the more ionizable mercury vapor can notpass through the quartz wall and therefore accumulates in the cathode.Inasmuch as helium has a diffusion rate more than seven times that ofmercury vapor the pressure of mercury vapor inside the cathode can becaused to preponderate greatly over its pressure outside the cathodeeven when using a porous wall of carbon which will pass the mercuryvapor to some extent. For certain classes of work the vacuum tube may befilled with helium to a pressure of the order of onehalf centimeter ofmercury and a small quantity of mercury (as little as a single drop insmall tubes) may be incorporated in the tube to supply the mercuryvapor. The ionization voltages of mercury and helium are ten andone-half volts and twenty-five volts respectively.

Thus the gas in the cathode may be more intensely ionized and therebyafford a lower voltage drop between the electrodes. The eifect may beaccentuated by intensely heating the gas in the cathode (e. g. 2800 C.or higher) as disclosed for example in my copending application SerialNo. 13,145 filed on even date herewith and in Serial No. 696,337 filedMarch 1, 1924. With the gas inside the cathode at high temperature manyof the atoms are in an excited state, that is their electrons aredisplaced from their orbits near the atomic nuclei to more remote orbitswithout being entirely removed from the influence of the nuclei, andconsequently electrons flowing from the inner surface of the cathodereadily ionize the gas in the cathode. Thus the voltage drop is reducedto a low value.

While other gases having different ionizing and diffusingcharacteristics oifer the same general advantages (e. g. hydrogen may beused instead of helium and caesium vapor, krypton or xenon may be usedinstead of mercury vapor) the above combination of gases offers specialadvantages. For example, helium offers a long mean free path asdisclosed in Serial No. 464,358 new Patent No. 1,617,174 grantedFebruary 8, 1927 and mercury may be incorporated in liquid form thusinsuring practically an inexhaustible supply of vapor.

In still another aspect the invention involves shielding the anode frompositive ion bombard-- ment during the portion of the cycle in which thecurrent tothe anode is small (e. g. in a rectifying tube, during thehalf-cycle in which the anode is negative), whereby the gaseousdischarge between the electrodes is more effectively restricted to onedirection in starting with the cathode cold, the helium shielding theanode from excessive bombardment by mercury ions during the half-cyclesof reverse voltage.

"The invention is particularly applicable to the rectification ofalternating current and rectifiers incorporating the invention arecharacterized by low voltage drop even when rectifying current ofmoderately high voltage, (e. g. one thousand volts and upward). For thepurpose of illustration the invention is shown as applied to a rectiflerin the accompanying drawing in which the figure represents, more or lessdiagrammatically, a longitudinal axial section of a rectifying tubecomprising an anode A, a cathode C, a shield S, a tube T and anelectro-magnet M encircling the tube. The aforesaid parts are preferablycylindrical in transverse section and coaxial. The tube T may be formedof hard or highly refractory glass and the electrodes A and C and theshield S of tungsten or other suitable material; and the electrodes andshield may be supported in the tube by any suitable means, stems a, c,and 8 being shown for that purpose. The anode A substantially enclosesthe cathode C and shield S and prevents radiations and materials fromescaping from the space so enclosed. D represents a drop of mercury orother vapor yielding material for supplying, either by normalevaporation or by application of external heat (e. g.

with a heating coil H), one of the aforesaid gases. When employinghelium at approximately one-half centimeter pressure a drop of mercurywill afford a suitable proportion of mercury vapor in the tube. Pdesignates the porous or semi-permeable membrane or wall hereinbeforereferred to. In the event membrane 1P comprises quartz or otherinsulating material, a conductor X is necessary between cathode C andstem 0; this lead is desirable, though not necessary,

in case member P is a semi-conductor, as carbon.

When using helium and mercury this wall is preferably formed of quartz,to permit the diffusion of helium therethrough without passing themercury vapor, and it may be anchored over the lower end of the hollowcathode C in any suitable manner.

With a suitable potential impressed between the cathode C and anode A anelectron stream fiows from the interior of the hollow cathode throughopenings E and L to the anode, the shield S serving to localize the heatproduced in the cathode by the current'fiow and thereby augmentingionization within the cathode as described in,-the aforesaid copendingapplications. The shield S also serves to localize the current flowalong a restricted path. Thus all 'the discharges which occur areconfined and pass from the interior of the cathode C through theopenings E and L to the anode A. When the magnet M is energized thefield thereby produced reacts with the field produced by said current,thereby rotating the gas inside the cathode. This rotation of the gasproduces a higher pressure adjacent the inner periphery of the cathode,thereby affording a higher state of ionization at the active surface ofthe cathode and facilitating electronic emission therefrom. By extendingthe stem c through the center of the cathode to a point adjacent theopening E, the gas inside the cathode is more effectively trapped andprevented from flowing out of the cathode along the axis thereof. Indeedthis construction results in gas flow into the cathode through openingE, which is in the nature of a continuous pumping action, therebymaintaining a higher average. pressure inside the cathode than outside.

Owing to the fact that the less ionizable gas (e. g. helium) diffusesthrough the well P the gas trapped in the hollow cathode ispredominantly the more ionizable component (e. g. mercury vapor),thereby further favoring current flow from the interior of the cathode.When the more ionizable gas is also heavier than the less ionizable gas(as mercury vapor is heavier than helium) the preponderance of the moreionizable gas adjacent the inner periphery of the hollow cathode isfurther augmented by the aforesaid centrifugal action.

The combined effect of the aforesaid factors. conducing to a high stateof ionization inside the cathode, is to make the interior of the hollowcathode a markedly effective source of electrons as disclosed in mycopending application Serial No.- 13,145 filed herewith. This effect maybe further accentuated by heating the cathode independently of thecurrent flow between cathode and anode or by coating the interiorsurface of the cathode with a high electron emitting material such ascaesium, whereby copious electron emission is produced at thetemperature at which the cathode surface is maintained. This coatinggives the interior surface of the cathode a low work function ascompared with the higher work function of the anode surface. The cathodemay also be maintained at a higher temperature by making its outersurface or the inner surface of the shield S highly reflecting or both.By making the inner surface of the cathode bright less light is absorbedby the cathode and ionization inside the cathode is further augmented.

For some purposes the present invention may advantageously incorporatethe mean free path principle disclosed in iny prior applications SerialNos. 406,866. 415,536, 526,095 etc., now Patent No, 1,545,207, grantedJuly 7, 1925 and Patents No. 1,617,171 and No. 1,617,179, grantedFebruary 8, 1927 in which case the distance between cathode C and shieldS or between shield S and anode A or both should be confinedsubstantially to the mean free path of electrons in the gas in thesespaces, that is, the average distance traveled by an electron ationizing velocity without ionizing impact with a gas molecule.

From the foregoing it is evident that the top portion of the cathodesurrounding the opening E constitutes an obstruction between theelectron emitting periphery of the cathode and the electron receivingsurface of the anode, and restricts the current flow to the opening E.

The features of invention relating to the mounting of the shield aroundthe anode and the spacing between the shield and the adjacent electrodesare not claimed in this application, but in my co-pending applicationsSerial No. 55,262, filed September 9, 1925, and Serial No. 76,792, filedDecember 21, 1925, which are as to these features continuations of thepresent application. The features of invention relating broadly to theuse of two gases having different ionizing voltages, and the maintenanceof the gas having a lower ionization voltage at higher density adjacentthe cathode surface than in the anode enemas region, are likewise notclaimed in the present application, but are made the subject matter ofmy co-pending application Serial No. 55,282, filed September 9, 1925,which is in this respect a continuation oi the present application.

I claim:

1. A gaseous discharge device comprising a tube containing an easilyionizable gas and a gas less easily ionizable but more difiusible, ananode, a hollow cathode having a discharge opening therein, said cathodehaving an obstructed passageway through which the less easily ionizablegas may escape more rapidly than the other gas, whereby when a dischargeoccurs, said gases will be pumped into the hollow cathode and allow theless easily ionizable gas to escape.

2. A gaseous discharge device comprising a tube containing an easilyionizable gas and a gas less easily ionizable but more diifusible, ananode, a hollow cathode having a discharge opening therein, said cathodehaving a porous wall through which the latter gas may escape morereadily whereby when the discharge occurs, said gases are pumped intothe cathode permitting the less easily ionizable gas to escape.

3. A unidirectional space current discharge device comprising anevacuated envelope containing a gas, a portion of which is more ionizedduring discharge than another portion of it, an anode, a cathodestructure having a discharge surface and constituting an enclosureconfining a body of gas in said envelope adjacent said dischargesurface, said enclosure having an opening for passing the discharge tosaid anode and having portions more permeable to the gas portion that isnot ionized than to the gas portion that is ionized.

4. A unidirectional space current discharge device comprising anevacuated envelope containing a filling of easily ionizable gas and adifficult-to-ionize gas, an anode, a cathode structure having adischarge surface and constituting an enclosure confining a body of saidgas filling in said envelope adjacent said discharge surface,

said enclosure having an opening for passing the discharge to saidanode, said enclosure aving a portion opposing outflow of said easilyionizable gas more than said dimcult-to-ionise gas.

5. A unidirectional space current d scharge device comprising anevacuated envelope containing a gas filling composed of a mixture ofdifferent gases, an anode, a cathode having a discharge surface andconstituting an enclosure confining a body of said gas filling in saidenvelope adjacent said discharge surface, said enclosure having anopening for passing the discharge to said anode, said enclosure havingportions of diilerent degrees of permeability for the different gases ofsaid mixture.

6. A space current discharge device comprising an evacuated envelopecontaining a gas, a portion of which is more ionized during thedischarge than another portion of it, an anode, and a cathode withinsaid envelope, an enclosure constituting a confinement around a part ofthe discharge path between said cathode and said anode, and meansadjacent to said enclosure to produce movement of gas into saidenclosure during a discharge, said enclosure having a portion ofdifferent permeability to the portion that is more ionized than to thegas portion that is less ionized.

7. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a cathode which during operation ismaintained at an elevated temperature to give copious electron emission,said cathode and anode being adapted to support an ionizing dischargebetween them, said cathode comprising an electron emitting surfaceadapted to be heated to a temperature of copious electron emission, anda hollow member surrounding said emitting surface, an opening ofsubstantial size in said hollow member. said anode having a surface 0!relatively high work iuncticn substantially closing said opening toprevent radiations and material liberated by the discharge from escapingfrom the space enclosed by said hollow member and said anode, said anodebeing insulated from said hollow member, all of the discharges whichoccur in said device being confined to the space enclosed by said hollowmember and anode.

8. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a cathode which during operation ismaintained at an elevated temperature to give copious electron emission,said cathode and anode being adapted to support an ionizing dischargebetween them, said cathode comprising an electron-emitting surfaceadapted to be heated to a temperature of copious electron emission, anda hollow conducting member electrically connected to and surroundingsaid emitting surface, and an opening of substantial size in said hollowmember, said anode having a surface of relatively high work functionsubstantially clomng said opening to prevent radiations and materialliberated by the discharge from escaping from the space enclosed by saidhollow member and said anode, all of the discharges which occur in saiddevice being confined to the space enclosed by said hollow member andanode.

9. A space discharge device comprising a gastight envelope containing anionizable atmosphere, an anode, and a cathode which during operation ismaintained at an elevated temperature to give copious electron emission,said cathode and anode being adapted to support an ionizing dischargebetween them, said cathode comprising an electron-emitting surfaceadapted to be heated to a temperature oi copious electron emission, anda hollow conducting member electrically connected to and surroundingsaid emitting surface, and an opening of substantial size in said hollowmember, said anode having a surface of relatively high work functionsubstantially closing said opening to prevent radiations and materialliberated by the discharge from escaping from the space enclosed by saidhollow member and said anode, said anode also having a relatively largearea exposed to the atmosphere outside of the space enclosed by saidhollow conducting member and said anode, all of the discharges whichoccur in said device being confined to the space enclosed by said hollowmember and anode.

10. A space discharge device comprising a gastight envelope containingan ionizable atmosphere, an anode, and a cathode which during operationis maintained at an elevated temperature to give copious electronemission, said cathode and anode being adapted to support an ionizingdischarge between them, said cathode comprising an electron-emittingsurface adapted to be heated to a temperature of copious electronemission, and a hollow conducting member electrically connected to andsurrounding said emitting surface, an opening in said hollow member,said anode having a surface substantially blocking said opening toprevent radiations and material liberated by the discharge from escapingfrom the space enclosed by said hollow member and said anode.

11. A space discharge device comprising a gastight envelope containingan ionizable atmosphere, an anode and a cathode which during operationis maintained at an elevated temperature to give copious electronemission, said cathode comprising an electron-emitting surface adaptedto be heated to a temperature of copious electron emission, and a hollowmember sur rounding said emitting surface, an opening in said hollowmember for allowing a discharge to pass from said emitting surface tosaid anode, said anode being disposed outside of said hollow member,said anode having a swim substantially blocking said opening.

12. A space discharge device comprising a gastight envelope containingan ionizable atmosphere, an anode and a cathode which during operationis maintained at an elevated temperature to give copious electronemission, said cathode comprising an electron-emitting surface adaptedto be heated to a. temperature of copious electron emission, and ahollow conducting member electrically connected to and surrounding saidemitting surface, an opening in said hollow member for allowing adischarge to pass from said emitting surface to said anode, said anodeiiaving a surface substantially blocking said open- CERTIFICATE OFCORRECTION.

Patent N00 2,157,198.,

CHARLES G, SMITH.

error appears in the printed specification It is hereby certified thatNovember 15, 1958.

of the above numbered patent requiring correction'as follows: Page 2,second column, line 10 for "well P" read wall P page5, first column,line 55, claim 5, afterthe word "cathode" insert structure; and line 71,claim 6, after "the" insert gas; and that the said lLetters Patentshould be read with this correction therein that the same may conform tothe record of the case in the Patent (lfffice Signed and sealed this27th day of December, A, D. 1958.

(Seal) Henry Van Arsdale Acting Comissloner of Patents.

